(663a) Bark-Based Biorefinery – From Pilot Experiments to Process Model

There is a growing interest in liquid biofuels produced from renewable biomass resources. The bioethanol used today is mainly produced from 1^st generation raw materials, such as sugar or starch crops. The abundance and relatively low cost combined with the non-food nature of agricultural, agro-industrial and forestry lignocellulosic residues make them attractive as 2^nd generation feedstock for large-scale production of bio-based fuels and chemicals. Currently, bioprocessing of lignocellulosic material is focused on enzymatic hydrolysis of the cellulose fraction to glucose, followed by fermentation and post-processing to fuel-grade ethanol. In this paper, the utilization of spruce bark as a lignocellulosic feedstock for a future integrated biorefinery was evaluated. The aim of this concept study was to develop a bark based biorefinery model exploiting results from pilot scale trials. The process concept consists of isolation of bark speciality compounds by water extraction and ethanol production by enzymatic hydrolysis and fermentation. The co-production of high value fine chemicals and ethanol may increase the economical attractiveness of the concept. This paper focuses mainly on water extraction of spruce bark to isolate polyphenols (tannin) and stilbene glycosides. Polyphenols and stilbene glycosides, naturally present in trees (bark, root, leaves), have been reported to possess antimicrobial, antibacterial, antifungal, antioxidant, anti-inflammatory, anticancer, and antimalarial activities, and have received much attention in nutraceutical, pharmaceutical, biochemical, food and cosmetic industry. The effect of extraction conditions on polyphenols and stilbene glycoside yields was studied in pilot scale. The extraction parameters considered were bark particle size, extraction time, temperature, and solid-liquid ratio. The choice of parameters and their values was based on preliminary lab and pilot scale experiments. Spruce bark was extracted in a batch reactor (100 L) with pure water at ambient pressure at temperatures below 100 °C. The extracted bark was pressed, and the obtained extract was separated from solids with a decanter centrifuge, and analysed to determine the stilbene glycoside and tannin concentrations. The paper discusses the challenges in the exploitation of laboratory and pilot scale experiments in unit operation modelling, and presents a process model of a bark-based biorefinery concept validated with results from the pilot experiments. The extraction results showed quite high variance. The contradiction between the results and common sense assumptions might be due to the inhomogeneous nature of bark, the unsuitability of the extractor used, poor repeatability of the experiments or problems in analytical methods. Especially the effect of bark particle size and extraction time on extraction yields remained partly unclear. This adds to the uncertainty of the model.